Flask



FIG. 1 is a top, rear and right side perspective view of a flask showing my new design;

FIG. 2 is a front elevational view thereof;

FIG. 3 is a rear elevational view thereof;

FIG. 4 is a left side elevational view thereof, the right side elevational view being a mirror image; and,

FIG. 5 is a top plan view thereof.

The broken lines shown in the drawing views are included for the purpose of showing environmental structure that forms no part of the claimed design. 

The ornamental design for a flask, as shown and described. 